The present invention concerns a method of and device for positioning an X-ray cassette in relation to an X-ray source.
The source of the X-rays employed for diagnostic purposes in emergency rooms in particular is mounted on a mobile structure. To take an X-ray picture the structure is moved to the vicinity of the patient's examining table. The patient to be X-rayed is then usually lifted by the emergency-room personnel and a cassette is slid under him or her. The cassette contains either a conventional X-ray film or an imaging plate containing stimulable elements such as a phosphor or fluorine. To make the exposure the source is positioned above the patent as precisely as possible in relation to the cassette. Once the picture has been taken, the cassette is removed from beneath the patient and the film or plate is removed from the cassette for processing. The conventional X-ray films are developed conventionally and the imaging plates are excited point by point by a beam of light, usually a laser. The stimulated light is sensed electro-optically, generating graphics signals that can be further processed digitally in a computer.
An X-ray cassette can be positioned in relation to a beam of X-rays generated by an X-ray source by means of a primary-radiation diaphragm as described in the European Patent No. 0,381,795. The diaphragm is mounted on an arm extending outward from the source. The diaphragm generates an apparent reticle that can be oriented with respect to a justification field. The justification field is accommodated in a compartment with marks that must be brought into coincidence with the reticle. The cassette itself is inserted into the compartment once the justification has been carried out, and the compartment is advanced below the patient table in a special cart.
One drawback of this approach is that it requires a relatively complicated cart to accommodate the cassette. The approach also requires special tables, which are not widely available and which are manufactured only in small quantities, which adds to the expense.